Attentional requirements is visual detection and identification: evidence from the attentional blink

The relationship between attention and consciousness: an expanded taxonomy and implications for 'no-report' paradigms

Tensions between global neuronal workspace theory and recurrent processing theory have sparked much debate in the field of consciousness research. Here, we focus on one of the key distinctions between these theories: the proposed relationship between attention and consciousness. By reviewing recent empirical evidence, we argue that both theories contain key insights and that certain aspects of each theory can be reconciled into a novel framework that may help guide future research. Alternative theories are also considered, including attended intermediate-level representations theory, integrated information theory and higher order thought theory. With the aim of offering a fresh and nuanced perspective to current theoretical debates, an updated taxonomy of conscious and non-conscious states is proposed. This framework maps a wider spectrum of conscious states by incorporating contemporary views from cognitive neuroscience regarding the variety of attentional mechanisms that are known to interact with sensory processing. Whether certain types of attention are necessary for phenomenal and access consciousness is considered and incorporated into this extended taxonomy. To navigate this expanded space, we review recent 'no-report' paradigms and address several methodological misunderstandings in order to pave a clear path forward for identifying the neural basis of perceptual awareness.This article is part of the theme issue 'Perceptual consciousness and cognitive access'.

The Attentional Blink is Susceptible to Concurrent Perceptual Processing Demands

In a rapid serial visual presentation stream processing of a first target (T1) impairs detection or identification of a second target (T2) that appears within 500 ms after T1. This effect characterizes the so-called attentional blink (AB). To evaluate contemporary information-processing accounts of the AB phenomenon in terms of the underlying processing mechanisms the present study examined the potential influence of Task 1 difficulty on the AB effect. To this end, T1 contrast and T1 response requirements were systematically varied across four experiments. Experiment 1 ruled out a mere sensory basis of the contrast manipulation on T2 performance. When only T2 had to be reported (Experiment 2) an AB effect occurred that was slightly modulated by T1 contrast. When report of both T1 and T2 was required in a standard AB task (Experiment 3), the magnitude of the AB depended to a larger extent on stimulus contrast, and it increased further when speeded T1 choice responses were additionally required (Experiment 4). On the basis of the present impact of Task 1 difficulty on the AB effect we conclude that processing limitations cause the AB phenomenon. We discuss such limitations in terms of perceptual (T1 consolidation) and central (response selection) bottleneck processes.

Effects of subtle stimulus strength on the attentional blink

The attentional blink refers to a type of impairment in detecting a second target (T2) after detecting a first target (T1) in rapid serial visual presentation (RSVP). Until recently, the role of T1 and how it is related to limitations in postperceptual processing such as selective attention and memory have been intensively studied. Here, we focus on the role of T2 and investigate whether an unnoticeable difference in the stimulus strength of T2, as indexed by the contrast of stimuli, can still influence this postperceptual process. We found that T2 performance was modulated by subtle T2 strength differences, although the T2 strength difference was not perceptually noticeable within the RSVP stream. These results suggest that T2 strength is important in the postperceptual stages of T2 processing-consolidation.

Alerting enhances target identification but does not affect the magnitude of the attentional blink

Identification of the second of two targets is impaired when presented less than about 500 ms after the first. The magnitude of this attentional blink (AB) is known to be modulated by tonic factors (e.g., observer's state of relaxation). The present work examined the effects of a phasic change in observer's state brought about by an alerting stimulus (an aggregate of faint rings) presented in temporal proximity to either letter-target inserted in a temporal stream (RSVP) of digit distractors. In four experiments, identification accuracy of each target was substantially improved by presenting the alerting stimulus either in the target's frame or in the preceding RSVP frame. However, alerting did not modulate the magnitude of the AB. The appearance of an alerting effect on the AB in Experiment 1 was ascribed to a ceiling effect in Experiment 2. Experiment 3 ruled out endogenous temporal cueing effects; Experiment 4 examined the temporal gradient of alerting. Independence of the alerting and AB effects suggests that the alerting stimuli and the letter targets may be processed along distinct visual pathways.

Dynamic crossmodal links revealed by steady-state responses in auditory-visual divided attention

Frequency tagging has been often used to study intramodal attention but not intermodal attention. We used EEG and simultaneous frequency tagging of auditory and visual sources to study intermodal focused and divided attention in detection and discrimination performance. Divided-attention costs were smaller, but still significant, in detection than in discrimination. The auditory steady-state response (SSR) showed no effects of attention at frontocentral locations, but did so at occipital locations where it was evident only when attention was divided between audition and vision. Similarly, the visual SSR at occipital locations was substantially enhanced when attention was divided across modalities. Both effects were equally present in detection and discrimination. We suggest that both effects reflect a common cause: An attention-dependent influence of auditory information processing on early cortical stages of visual information processing, mediated by enhanced effective connectivity between the two modalities under conditions of divided attention.

Evidence for attentional processing in spatial localization

Using a dual-task methodology, this study examined the involvement of selective attention in spatial localization. Thirty participants located a single, briefly presented, peripheral target stimulus, appearing in one of 50 positions on either side of a central fixation point, with or without the requirement to identify a simultaneously presented central distractor stimulus. Results revealed a robust interference effect in localization performance at short target durations that depended on the number of the to-be-identified distractor items. This outcome provides convergent support for the role of the attentional system in spatial localization.

The reconfiguration of task set has no effect on the efficiency of feature search

In this study, we investigated whether or not the reconfiguration of a set task could modulate the efficiency of feature search. In Experiment 1, target set size was manipulated. The results revealed that enumerating targets defined by color yields a much steeper slope when executed simultaneously with a discrimination task than when done singly. However, when distractor set size was manipulated, there was no significant difference in the efficiency of individualizing targets from distractors between the two task conditions, no matter whetherthe search was guided by bottom-up information (Experiment 2) or top-down information (Experiment 3). Drawing upon these results, the authors propose that (1) an additional task can impair the efficiency of enumeration, resulting in a steep slope of counting even when target set size is quite small, and (2) in feature search, the visual system first reconfigures the task set to match the input feature information and then detects the targets with an optimal efficiency, which does not support the theory proposed by Di Lollo, Kawahara, Zuvic, and Visser (2001; Di Lollo, Smilek, Kawahara, & Ghorashi, 2005).

Effect of distractor sounds on the auditory attentional blink

Four experiments were conducted to determine whether or not the presence and placement of distractors in a rapid serial auditory stream has any influence on the emergence of the auditory attentional blink (AB). Experiment 1 revealed that the presence of distractors is necessary to produce the auditory AB. In Experiments 2 and 3, the auditory AB was reduced when the distractor immediately following the probe was replaced by silence but not when the distractor following the target was replaced by silence. Finally, in Experiment 4, only a very small auditory AB was found to remain when all distractors following the probe were replaced by silence. These results suggest that the auditory AB is affected both by the overwriting of the probe by the distractors following it and by a reduction in discriminability generated by all of the distractors presented in the sequence.

The meaning of the mask matters: evidence of conceptual interference in the attentional blink

The rapid serial visual presentation (RSVP) experiment reported here investigated the role of conceptual interference in the attentional blink (AB). Subjects were presented with RSVP streams that contained five stimuli: Target 1, a distractor, Target 2, a second distractor, and a symbol mask. Target 1 was a green letter, Target 2 was a red letter, and the distractors were either white letters or white digits. The stimuli were presented in a font typically seen on the face of a digital watch. Thus, "S" and "O" were identical to "5" and "0," respectively. This allowed us to present streams that were conceptually different even though featurally identical: The two letter targets were followed by distractors that were recognized either as "5" and "0" or as "S" and "O." The AB was substantially attenuated when subjects were told the distractors were digits rather than letters. This result indicates that conceptual interference plays a role in the AB.

Phase synchronization analysis of EEG during attentional blink

The attentional blink (AB) phenomenon occurs when perceivers must report two targets embedded in a sequence of distracters; if the first target precedes the second by 200-600 msec, the second one is often missed. We investigated AB by measuring dynamic cross-lag phase synchronization for 565 electrode pairs in 40-Hz-range EEG. Phase synchrony, on average, was higher in experimental conditions, where two targets are reported, than in control conditions, where only the second target is reported. The effect occurred in electrode pairs covering the whole head. Timing of the synchrony was crucial: Brief episodes of enhanced synchrony occurred 100-500 msec before expected target onset in AB conditions where the second target was correctly reported. These results show that intrinsic brain dynamics produce anticipatory synchronization in transient assemblies of cortical areas. Enhanced levels of anticipatory synchronization occur in response to the demands of the task in conditions where the system's limited capacity is under strain.

Delayed Masking and the Auditory Attentional Blink

The attentional blink (AB) corresponds to a transient deficit in reporting the second (T2) of two targets embedded in a rapid sequence of distractors. The retrieval competition ( Shapiro, Raymond & Arnell, 1994 ) and bottleneck models ( Chun & Potter, 1995 ; Jolicœur, 1998 ) predict the attenuation of the deficit with the extension of the delay between T2 and its mask. This prediction was tested using auditory sequences of nonverbal stimuli in which the T2-mask interval was systematically varied. The magnitude of the auditory AB diminished with the lengthening of the interval from 50 to 150 ms while no time-locked deficit was observed with the longest (350 ms) and the shortest (10 ms) intervals. These results suggest that presenting a mask after T2 is not sufficient to produce an auditory AB: The mask must be perceivable as an auditory event distinct from the target and occur before T2 consolidation. The present study also provides evidence that as in vision, AB deficits take place in the auditory domain when T2 is masked by interruption but not by integration. Our findings are best accounted for in terms of bottlenecked processing limitations.

Effect of attention on the detection and identification of masked spatial patterns

The effect of attention on the detection and identification of vertically and horizontally oriented Gabor patterns in the condition of simultaneous masking with obliquely oriented Gabors was studied. Attention was manipulated by varying the set size in a visual-search experiment. In the first experiment, small target Gabors were presented on the background of larger masking Gabors. In the detection task, the effect of set size was as predicted by unlimited-capacity signal detection theory. In the orientation identification task, increasing the set size from 1 to 8 resulted in a much larger decline in performance. The results of the additional experiments suggest that attention can reduce the crowding effect of maskers.

Mask-dependent attentional cuing effects in visual signal detection: the psychometric function for contrast

A spatial-cuing paradigm was used to test the hypothesis of Carrasco, Penpeci-Talgar, and Eckstein (2000) that the mask-dependent cuing effects found in visual signal detection by Smith (2000a) were caused by submaximal activation of the transient-orienting system. Mask-dependent cuing was found with a range of stimulus contrasts with pure peripheral cues and with the mixed central-peripheral cues of Smith (2000a), contrary to the predictions of the submaximal activation hypothesis. The use of a pedestal detection task to control spatial uncertainty showed that the cuing effect was due to signal enhancement. A model of mask-dependent cuing is described, which assumes that attention affects the rate of information accumulation from the display and that masks limit the visual persistence of the stimulus. The model correctly predicts differential mask dependencies in sensitivity for detection and discrimination and the associated patterns of response times.

Affective Influences on the Attentional Dynamics Supporting Awareness

Identification of a 1st target stimulus in a rapid serial visual presentation sequence leads to transient impairment in report for a 2nd target; this is known as the attentional blink (AB). This AB impairment was substantially alleviated for emotionally significant target words. AB sparing was not attributable to a variety of nonaffective stimulus factors that could result in augmented distinctiveness. Arousal value, not the valence of stimulus events, was found to be responsible for AB sparing. These results suggest that arousal is associated with decreased attentional prerequisites for awareness, enabling emotional significance to shape perceptual experience.

Object file continuity predicts attentional blink magnitude

When asked to identify targets embedded within a rapid consecutive stream of visual stimuli, observers are less able to identify the second target (T2) when it is presented within half a second of the first (T1); this deficit has been termed the attentional blink (AB). Rapid serial visual presentation methodology was used to investigate the relationship between the AB and object files (episodic representations implicated in object identification and perceptual constancy). An inverse linear relationship was found between the degree of object file continuity and AB magnitude. An important locus of object file continuity was the intervening stream items between T1 and T2. The results are discussed in terms of the heuristic of the object file to preserve limited attentional capacity.

The Attentional Dynamics of Masked Detection

A dichoptic masking procedure was used to test whether the mask-dependent cuing effects found in luminance detection by P. L. Smith (2000a) were due to integration masking or interruption masking. Attentional cuing enhanced detection sensitivity (d') when stimuli were backwardly masked with either dichoptic or monoptic masks, whereas no cuing effect was found with unmasked stimuli, implying the mask dependencies were due to interruption of stimulus processing in visual cortex by the mask. The effect is predicted by a gated diffusion process model in which masks interrupt stimulus processing and attention controls the flow of information to a sequential-sampling decision mechanism. The model correctly predicts different patterns of performance for detection and discrimination and cuing effects in simple reaction time.

Task switching mediates the attentional blink even without backward masking

When two targets are presented in rapid succession, perception of the second target is impaired at short intertarget lags (100-700 msec). This attentional blink (AB) is thought to occur only when the second target is backward masked. To the contrary, we show that task switching between the targets can produce an AB even without masking (Experiments 1 and 3). Further, we show that task switching produces an AB only when the second target does not belong to a class of overlearned stimuli such as letters or digits (Experiments 1 and 4). When the second target is masked, however, an AB is invariably obtained regardless of switching or overlearning. We propose that task switching involves a time-consuming process of reconfiguration of the visual system, during which the representation of the second target decays beyond recognition, resulting in an AB deficit. We suggest that overlearned stimuli are encoded in a form that, while maskable, decays relatively slowly, thus outlasting the delay due to reconfiguration and avoiding the AB deficit.

Visual masking during the attentional blink: tests of the object substitution hypothesis

When 2 masked targets are presented in a rapid sequence, correct identification of the 1st hinders identification of the 2nd. Visual masking of the 2nd target plays a critical role during this 2nd-target deficit, or "attentional blink" (AB). The object substitution hypothesis (B. Giesbrecht & V. Di Lollo, 1998) predicts that late-stage visual processes involved in object substitution mediate masking of the 2nd target during AB, whereby stronger masking should produce a more severe deficit. Six experiments are presented, together testing this hypothesis. Although masking by object substitution was observed, it did not interact with the AB. An alternative hypothesis is proposed stating that mostly early-stage visual processes mediate the masking effects that are critical to the AB.

The dark side of visual attention

The limited capacity of neural processing restricts the number of objects and locations that can be attended to. Selected events are readily enhanced: the bright side of attention. However, such focal processing comes at a cost, namely, functional blindness for unattended events: the dark side of visual attention. Recent work has advanced our understanding of the neural mechanisms that facilitate visual processing, as well as the neural correlates of unattended, unconscious visual events. Also, new results have revealed how attentional deployment is optimized by non-visual factors such as behavioral set, past experience, and emotional salience.